High-temperature titanium alloys have been widely used in aerospace engines due to their excellent thermal strength and high specific strength. Similar high-temperature alloy materials will be trump materials for a long time in the future. In today's rapidly changing science and technology, the research and future development of high-temperature alloy materials have high practical and strategic significance. Future aerospace vehicles and their thrust systems require the development of high-temperature alloy materials with higher strength, operating temperature and elastic modulus, lower density and lower price than the existing Ti64 and T16242 alloys. Therefore, high-temperature alloy materials are the mainstream development of aviation materials.
Definition of high temperature alloys
High-temperature alloys refer to metal materials based on iron, nickel, and cobalt that can adapt to short-term or long-term use in different environments under high temperatures above 600°C and certain stress. It also has higher high temperature strength, plasticity, good resistance to oxidation and hot corrosion, good thermal fatigue performance, fracture toughness and other comprehensive properties. High-temperature alloys have a single austenite structure and have good structural stability and service reliability at various temperatures. Based on the above performance characteristics and the high degree of alloying of high-temperature alloys, it is called superalloy in Britain and the United States.
Characteristics of high temperature alloy processing
For high-temperature alloys such as nickel alloys, titanium alloys and cobalt alloys, the high-temperature resistance directly increases the difficulty of processing. Under the combined action of heavy cutting force and high temperature generated during machining, the tool will be fragmented or deformed, causing the tool to break. In addition, most of these alloys rapidly develop work hardening. The hardened surface produced during machining of the workpiece will cause the cutting edge of the tool to notch in the depth of cut and cause undesirable stress in the workpiece, destroying the geometric accuracy of the machined parts. Processing titanium alloys also faces these problems. Although the cutting force required to machine titanium alloys is only slightly higher than that of steel, the special properties of titanium alloys make it much more difficult to machine than steel of the same hardness.
The main points are as follows:
1) Titanium alloys, like other high-temperature alloys, are also prone to work hardening;
2) The thermal conductivity of titanium-based alloys is very low, making almost all the heat generated during processing concentrated on the cutting edge;
3) The elastic modulus of titanium alloy is very small, especially under heavy cutting forces, making the workpiece susceptible to tool deflection and vibration;
4) The most serious thing is that the chemical properties of titanium alloy are more active than other high-temperature alloys, which makes the titanium alloy workpiece easily react chemically with the tool during processing, resulting in shrinkage cavities in the workpiece.
Because of the reasons above, processing high-temperature resistant alloys requires special processing technology.